As far as the late speech and walking and then an explosion of ability, is your DS a perfectionist? I think some of our kiddos who tend toward perfectionistic sometimes wait to show their abilities in things until they are certain they can do it well enough. Then there is also that whole Einstein theory/late-talker theory that these kids brains are so focused on more analytical and mathmatical tasks that their verbal and/or physical development can take a back seat for a while.

She thought she could, so she did.